The present invention relates to a telescopic unit which is capable of preventing rattling of the telescopic unit when in use. The invention also relates to a tripod provided with said telescopic units.
Examples of conventional telescopic units used for a tripod include one having a structure which calls for disposing a second tubular member in a first tubular member in such a way that the distance by which the second tubular member projects from the first tubular member can be adjusted, fixing an operation lever supporting member to the outer cylindrical surface of the lower end of the first tubular member, operating the operation lever supported by said operation lever supporting member so that a brake is pressed against the outer surface of the second tubular member. As a result of the brake being pressed against the second tubular member, the second tubular member is secured to the first tubular member.
However, the telescopic unit described above presents several problems; inclusion of a securing device that consists of an operation lever, an operation lever supporting member and a brake as a means to secure the second tubular member to the first tubular member results in a complex structure. Furthermore, as operating the operation lever each time is troublesome and makes the telescopic unit inconvenient to operate.
Examples of conventionally known devices to solve the above problems although it is of a simple structure as it is not provided with a securing device which consists of an operation lever and other members include a telescopic unit that is capable of easily securing the second tubular member by rotating the second tubular member relative to the first tubular member.
An example of such telescopic units used for tripods is shown in FIG. 12. The telescopic unit shown in FIG. 12 includes a first tubular member 2. A receiving portion 1 that tapers downward is formed at the lower end of the first tubular member 2 so as to prevent undesirable displacement of the first tubular member 2. A second tubular member 3 is positioned in the first tubular member 2 so as to be capable of rotating circumferentially and enabling the adjustment of the distance by which the second tubular member 3 projects from the first tubular member 2. A cam shaft member 4 is screwed to the top of the second tubular member 3, and a cam 5 having a partially cutout cylindrical shape is fitted around the cam shaft member 4.
When the second tubular member 3 is rotated in one direction circumferentially relative to the first tubular member 2, the cam shaft member 4 rotates together with the second tubular member 3. As a result, the cam 5 flares so that a press applying surface 5a of the cam 5 becomes pressed against the inner surface of the first tubular member 2, thereby securing the second tubular member 3 in the first tubular member 2.
However, as the second tubular member 3 is secured in the first tubular member 1 merely by the press applying surface 5a of the cam 5 pressed against a part of the cylindrical inner surface of the first tubular member 2, the conventional telescopic unit shown in FIG. 12 sometimes presents a problem of rattling of the telescopic unit when in use due to insufficient securing force.
In order to solve the above problem, an object of the present invention is to provide a telescopic unit which is not only of simple structure that is convenient to handle but also ensures sufficient securing force to prevent rattling when in use. Another object of the invention is to provide a tripod having the same effects as above.
A telescopic unit according to the present invention includes a first tubular member and a second tubular member, which is inserted in the first tubular member so as to be capable of rotating in the circumferential directions and enabling the adjustment of the distance by which the second tubular member projects from the first tubular member, wherein one or more press receiving surface portions are formed on the inner cylindrical surface of the first tubular member, said press receiving surface portions having a cross section which has an arc-shaped surface such that the center axis of the arc extends in parallel with the center axis of said first tubular member; one or more press applying surface portions are formed on the outer cylindrical surface of the second tubular member, said press applying surface portions having a cross section which has an arc-shaped surface such that the center axis of the arc extends in parallel with the center axis of said second tubular member; rotation of the second tubular member in one direction circumferentially relative to the first tubular member causes given locations of the press applying surface portions to be pressed against the press receiving surface portions, thereby securing the second tubular member to the first tubular member; and rotation of the second tubular member in the other direction circumferentially relative to the first tubular member releases the press applying surface portions and the press receiving surface portions from the press-contact with each other so that the distance by which the second tubular member projects from the first tubular member can be adjusted. With the configuration as above, in the state where the second tubular member is secured to the first tubular member, the press applying surface portions of the second tubular member are pressed against the press receiving surface portions of the first tubular member with securing force that is sufficient compared with the conventional art. As a result of the configuration described above, the present invention provides a telescopic unit which is of simple structure and convenient to handle and, by means of said sufficient securing force, capable of preventing rattling when in use.
According to another feature of the invention, a plural number of press receiving surface portions are formed on the inner surface of the first tubular member of the telescopic unit so that the press receiving surface portions are arranged in the circumferential direction with a distance between each press receiving surface portion and its adjacent press receiving surface portion, and a plural number of press applying surface portions are formed on the outer surface of the second tubular member of the telescopic unit so that the press applying surface portions are arranged in the circumferential direction at locations respectively corresponding to said press receiving surface portions, with a distance between each press applying surface portion and its adjacent press applying surface portion. With the configuration as above, press-contact between each press applying surface portion and the press receiving surface portion which faces the press applying surface portion ensures sufficient securing force distributed in the circumferential direction.
According to yet another feature of the invention, a receiving step portion is formed between each press receiving surface portion and its adjacent press receiving surface portion of the first tubular member, and a catching step portion that is adapted to catch the corresponding receiving step portion when the second tubular member is rotated circumferentially in the aforementioned other direction relative to the first tubular member is formed between each press applying surface portion and its adjacent press applying surface portion of the second tubular member. As the catching step portions of the second tubular member catch the receiving step portions of the first tubular member when the second tubular member is rotated in the other direction circumferentially relative to the first tubular member, the second tubular member is prevented from rotating more than necessary and is therefore free from the problem of becoming undesirably secured.
According to yet another feature of the invention, the first tubular member is provided with a receiving member which is snugly fitted in the bottom of the first tubular member and has a cross section having a shape similar to that of the first tubular base member, and the second tubular member is provided with a catching member which is snugly fitted around the outer surface of the upper end of the second tubular member, has a cross section having a shape similar to that of the second tubular member and is adapted to catch said receiving member when the second tubular member projects to its fullest extent. As the catching member of the second tubular member catches said receiving member of the first tubular member when the second tubular member projects to its fullest extent, the structure described above ensures reliable prevention of undesirable displacement of the second tubular member.
A telescopic unit according to yet another feature of the invention includes a first tubular member whose cross section is in the shape of an involute curve or a similarly shaped curve, and a second tubular member which is inserted in the first tubular member so as to be capable of rotating in the circumferential directions and enabling the adjustment of the distance by which the second tubular member projects from the first tubular member and has a cross section that is in the shape of an involute curve or a similarly shaped curve and corresponds to the cross section of the first tubular member, wherein rotation of the second tubular member in one direction circumferentially relative to the first tubular member causes the outer surface of said second tubular member to be pressed against the inner surface of the first tubular member, thereby securing the second tubular member to the first tubular member; and rotation of the second tubular member in the other direction circumferentially relative to the first tubular member releases the outer surface of the second tubular member and the inner surface of the first tubular member from the press-contact with each other so that the distance by which the second tubular member projects from the first tubular member can be adjusted. With the configuration as above, in the state where the second tubular member is secured to the first tubular member, the outer surface of the second tubular member, whose cross section is in the shape of an involute curve or a similarly shaped curve, is pressed against the inner surface of the first tubular member, whose cross section is in the shape of an involute curve or a similarly shaped curve, with securing force that is sufficient compared with the conventional art. As a result of the configuration described above, the present invention provides a telescopic unit which is of simple structure and convenient to handle and, by means of said sufficient securing force, capable of preventing rattling when in use.
A telescopic unit according to yet another feature of the invention includes a first tubular member whose cross section has a shape comprised of a combination of identical parts of either an involute curve or a similarly shaped curve, and a second tubular member which is inserted in the first tubular member so as to be capable of rotating in the circumferential directions and enabling the adjustment of the distance by which the second tubular member projects from the first tubular member and has a cross section whose shape corresponds to that of the first tubular member and is comprised of a combination of identical parts of either an involute curve or a similarly shaped curve, wherein rotation of the second tubular member in one direction circumferentially relative to the first tubular member causes the outer surface of said second tubular member to be pressed against the inner surface of the first tubular member, thereby securing the second tubular member to the first tubular member; and rotation of the second tubular member in the other direction circumferentially relative to the first tubular member releases the outer surface of the second tubular member and the inner surface of the first tubular member from the press-contact with each other so that the distance by which the second tubular member projects from the first tubular member can be adjusted. With the configuration as above, in the state where the second tubular member is secured to the first tubular member, the outer surface of the second tubular member, whose cross section has a shape comprised of identical parts of either an involute curve or a similarly shaped curve, is pressed against the inner surface of the first tubular member, whose cross section has a shape comprised of a combination of identical parts of either an involute curve or a similarly shaped curve, with securing force that is sufficient compared with the conventional art. As a result of the configuration described above, the present invention provides a telescopic unit which is of simple structure and convenient to handle and, by means of said sufficient securing force, capable of preventing rattling when in use.
A tripod according to the invention includes a base which is provided with leg attachments, and telescopic units which are in accordance with any one of the features of the invention described above and respectively attached to said leg attachments. By using telescopic units attached to the leg attachments of the base as the legs of a tripod, it is possible to prevent rattling of the tripod when in use.